A vehicle usually includes a variety of connection assembly to attach different parts and panels. For example, a wiring holder assembly is used to glasp the wiring in the vehicle. In another example, a trim panel assembly is used to fix the trim panel to a vehicle door. A connector is usually connected to an assembling bracket via a clip or a sliding rail. However, a gap usually exists between the connector and the assembling bracket and thus the connector cannot rest on the assembling bracket firmly. When the vehicle is bumping, the collision between the connector would generate squeak and rattle. Further, the connector and the assembling bracket may be worn out after long time of use.